This article mainly introduces three hazards of using expired PCB.

01

Expired PCB may cause surface pad oxidation
Oxidation of the soldering pads will cause poor soldering, which may eventually lead to functional failure or risk of dropouts. Different surface treatments of circuit boards will have different anti-oxidation effects. In principle, ENIG requires it to be used up within 12 months, while OSP requires it to be used up within six months. It is recommended to follow the shelf life of the PCB board factory ( shelflife) to ensure quality.

OSP boards can generally be sent back to the board factory to wash off the OSP film and re-apply a new layer of OSP, but there is a chance that the copper foil circuit will be damaged when the OSP is removed by pickling, so it is best to contact the board factory to confirm whether the OSP film can be reprocessed.

ENIG boards cannot be reprocessed. It is generally recommended to perform “press-baking” and then test whether there is any problem with the solderability.

02

Expired PCB may absorb moisture and cause board burst

The circuit board may cause popcorn effect, explosion or delamination when the circuit board undergoes reflow after moisture absorption. Although this problem can be solved by baking, not every kind of board is suitable for baking, and baking may cause other quality problems.

Generally speaking, OSP board is not recommended to bake, because high-temperature baking will damage the OSP film, but some people have also seen people take OSP to bake, but the baking time should be as short as possible, and the temperature should not be too high. It is necessary to complete the reflow furnace in the shortest time, which is a lot of challenges, otherwise the solder pad will be oxidized and affect the welding.

03

The bonding ability of expired PCB may degrade and deteriorate

After the circuit board is produced, the bonding ability between the layers (layer to layer) will gradually degrade or even deteriorate over time, which means that as time increases, the bonding force between the layers of the circuit board will gradually decrease .

When such a circuit board is subjected to high temperature in the reflow furnace, because circuit boards composed of different materials have different thermal expansion coefficients, under the action of thermal expansion and contraction, it may cause de-lamination and surface bubbles. This will seriously affect the reliability and long-term reliability of the circuit board, because the delamination of the circuit board may break the vias between the layers of the circuit board, resulting in poor electrical characteristics. The most troublesome is Intermittent bad problems may occur, and it is more likely to cause CAF (micro short circuit) without knowing it.

The harm of using expired PCBs is still quite large, so designers still have to use PCBs within the deadline in the future.